1. IP.
We start from IP, later TCP/IP etc.

     IP means Internet Protocol, and its the principal protocol used on the net. Internet means inter-networks, which means betweens the networks, this is one big interconnection of the networks all around the world. The Internet Protocol (IP) gives those networks the abillity to communicate in between.

     Lets make an exemple with the post.
When you want to send a letter through the post:

• You put your letter in envelope.
• Your write the address of the addressee.
• You write your name there too.

                                    Â

Those are the regle utilised by everyone. This is protocol!
In internet, it's almost the same. Each message, each little packet is in some envelope that give different information:

• Your IP.
• Destinate IP.
• Something.

     The IP addresse is unique possesion of each computer on Internet. That means there are no 2 computers with the same IP. (Yes sometimes they are same, but all exist from one other IP).
The IP is normally in the form of 4 digits (from 0 to 255), divised by four points (.) -> e.g 84.43.140.239

1.2. The routing.

    When send your letter, you put it in the near mailbag, then someone take it to the centre of your city, the post, then someother citys, and finnaly it arrives to the destinaire.

                                   

It is the same on the net. You put the IP packet to your near server, and then he will pass from PC to PC untill he reaches the destinate pc.

                                   


1.3. Peer to Peer

                                   

    The peer-to-peer, called p2p, computer network is something typically used for connecting someone to somelse. A to B. Such networks are useful for sharing different files (music, video, data, movies, and whatever you wish including realtime data such as telephony traffic). Originally p2p dont need server, both clients are playing different roles, one is server, other client. This model is different from the client <-> server <-> client model, where the server is the big guy who brings the clients together. Classic exemple is the FTP Server. Other networks are based both on p2p and cliend-server-client structures (like IRC).

2. The ports

Okay, with IP we can send many things. But imagine that many many programs work on a single PC, and a packet is sended to this PC. So if the computer recives it, will he know to which program it is (this packet).

                                   

This is a serious problem to resolve. Okay, we can mark each process on our computer with some number and then put the same number in the IP packet. We call those numeros "Ports", its like the numeros uniques of the houses.

                                   

This way the IP shows where to go the packet, and the Port shows for which program it is.

3. UDP/IP

UDP means 'User Datagram Protocol', and it's a protocol that allows to utilize ports with IP addresses. IP engage with the addresses, and UDP engage with ports. With UDP we can send data from Program X/Address A  to Program Y/Address B.

Okay, lets send something to fuzzy's server, on port 600:

                                   

As you see, each layer add his information. IP information allows to locate fuzz's server, and the port carried by UDP will show the right application (here the Fuzzy's server).
This pair IP:

• 84.43.140.239
• 213.91.244.212

we call it "socket".

3. TCP

TCP means 'Transmission Control Protocol' And it can:

• Do everything that UDP can.
• Verify if the reciever is ready to recive.
• Split those big packets and make them smaller, that way IP can accept
• Numerate those packets and be sure that they are recived, to ask again for those packets which are missing.

For an exemple the message "I love you" will look like:

                                   

Not bad eh? TCP/IP could is used for many other things.

• FTP uses TCP/IP.
• In your browser, the protocol HTML uses TCP/IP for his needs (Recieving and Sending pages, images, etc).
• Your browser, and someother things, uses the DNS protocol to find an IP address from some name (e.g cable-84-43-140-239.mnet.bg to 84.43.140.239, or aeshells.org to 65.23.157.184). The DNS protocol uses TCP\IP for his needs.
• Your email which uses STMP and POP3 for sending and recieving mails. STMP and POP3 uses TCP\IP too.

4. The layer model.

As you now know:

• The data from different applications is enveloped by TCP
• TCP itself is eveneloped by IP
• And this IP packet can be eveloped too by PPP (point to point protocol) or Ethernet, or whatever..

The communication pass through different layers:

• Each layer has some mission: verify, routing, conversion etc.
• Each layer communicate with upper and down layer.
• Each layer envelope the data from upper layer, adding his new information, before pass it to down layer.

An exemple: TCP layer send information to Someserver who is down, using the upper IP layer.

4.1 The OSI model.

OSI = Open Systems Interconnection. Understanding this is the key for understanding the network itself.

This is a model who is compound by seven (7) layers who have their role.

                                   




Some notes:
- Everyperson, each IP and event here are NOT accidental
- Fuzzy is starring fuzzy.
- Alex is starring alex.
- icetrax is starring me.

LoL!